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3. TECHNICAL BRIEF
3.3 26 MHz Clock (VCTCXO, X500)
The 26 MHz clock(X500) consists of a TCXO(Temperature Compensated Crystal Oscillator) which
oscillates at a frequency of 26 MHz. It is used within the Si4205, digital base band chipset
(U101, AD6527)
C530
100p
3.4 Power Supplies for RF Circuits (RF LDO, U503)
Two regulators are used for RF circuits. One is MIC5255 (U503), and the other is one port of AD6537B
(U102).
MIC5255 (U503) supplies power to transceiver (SI4205, U505). One port of AD6537B supplies power
to VCTCXO (X500). Main power (VBAT) from battery is used for PAM (SKY77325, U501) because
PAM requires high power.
Supplier
U503(VRF)
U102(VVCXO)
Battery(VBAT)
Figure 3-6 VCTCXO CIRCUIT DIAGRAM
2V75_VVCXO
X500
R510
3
OUT
VCONT
100
4
VCC
GND
C533
26MHz
2.2u
Table 3-2 RF POWER SUPPLIERS
Voltage
2.85 V
2.75 V
3.4 ~ 4.2 V
- 22 -
R511
1
10K
2
C531
0.1u
Powers
U505, U501
X501
U501, U503
AFC
enabled signal
CLKON
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